Non-fragile, compressible consumer products such as disposable diapers and training pants, feminine hygiene pads, disposable adult incontinence pads and pants, and wipes and cloths for baby and personal cleansing and household cleaning, are often packaged and sold at retail (i.e., placed on display and for sale in a retail store) in soft packages or bags formed of polymer film. Such packages are often formed from one or more sheets of polymer film, with edges joined at seams via application of heat, which has caused the film to melt and fuse along the seams.
It is often desired that packaging film be amenable to seaming via application of heat in such a manner that thorough fusing and sealing will occur, while at the same time, dramatic deformation of the film in the seaming equipment will not occur. This capability may be desired so that the seams formed are mechanically strong for package structural integrity, and the seams are substantially sealed or airtight to help protect the contents from humidity and contamination, e.g., by entry of dust into the package. In conjunction, it is desirable that the polymer film material will not melt so much as to separate from the film sheet and foul the seaming equipment, and that the film material will substantially retain its dimensions and appearance through or across the seam.
It is often desired that a film to be used to form a retail package have as much opacity as can be achieved, for purposes of imparting a robust appearance to the package, for purposes of concealment of the contents, for purposes of preventing appearance of the contents from visually interfering with outward appearance of printed material on the package and/or for purposes of reducing a need for opacity of (and associated expense for) inks that may be used for printing colored package artwork, graphic designs and/or characters and text constituting branding, labeling and product information. It is also often desired that a package film material have a bright white color, for purposes of imparting a new, fresh and clean appearance to the package and/or for purposes of providing a bright neutral background for colored printing.
Finally, for purposes of providing a structurally robust package while also exercising economy in consumption of polymer materials, it is usually desired that a packaging film have as much mechanical (tensile) strength, seamability, opacity, and whiteness, as possible, while having the lowest caliper (thickness) as possible and practical.
Maximizing all of these desirable features and properties of a packaging film requires use of materials and methods in ways that are not mutually complementary and cost effective. Inclusion of inorganic opacifying and/or whitening agents will typically compromise a polymer film's tensile strength, yield stress and ability to fuse cleanly and neatly with application of heat, to form seams with structural integrity and good sealing. Commonly used inorganic opacifying and whitening agents, such as preparations containing particles of titanium dioxide (TiO2) and/or calcium carbonate (CaCO3), are both abrasive to film extruding equipment, and add substantial cost. As caliper and basis weight of a film material is decreased, seamability may be compromised, and tensile strength and opacity are decreased.
In view of these competing objectives, there is room for improvement in formulation of materials and manufacture of packaging films that are required to be easily seamable via application of heat, be highly opaque, and have a bright white color. Prior attempts to impart opacity and/or whiteness, such as, for example, those described in U.S. Pat. Nos. 5,091,236; 5,261,899; 5,800,913 and European Patents Specification Nos. EP 0 388 086 and EP 0 473 573, have had only limited success.